Differential fluctuation in virulence and VOC profiles among different cultures of entomopathogenic fungi

Insect-passaged cultures of entomopathogenic fungi grown on potato dextrose agar media have been shown to have altered virulence and profiles of volatile compounds. The present study demonstrated the pathogenic status of FS0 (in vitro) and FS1 and FS2 (insect-passaged cultures grown on PDA) cultures of Metarhizium anisopliae (strains 406 and 02049) and Beauveria bassiana by a non-choice assay, in which filter paper was inoculated with fungal spores at a concentration of 1 × 107 spores/ml. The FS1 and FS2 cultures of M. anisopliae strain 02049 and B. bassiana produced conidia with high virulence, and the volatile profiles of these conidia comprised relatively lower percentages of branched-alkanes than conidia from the FS0 cultures. In contrast, the conidia from an FS0 culture of M. anisopliae strain 406 had somewhat elevated virulence levels, but their volatile profile had <2% branched-alkanes. The FS1 and FS2 cultures of M. anisopliae strain 406 did not gain virulence, and these cultures showed a decline in virulence along with major alteration of their volatile profiles. Their volatile profiles mainly comprised branched-alkanes. The volatile profiles of the FS1 and FS2 cultures lacked n-tetradecane, which was an important component of all the virulent cultures. Four compounds, 2-phenylpropenal, 2,5,5-trimethyl-1-hexene, n-tetradecane and 2,6-dimethylheptadecane, were detected only from the virulent cultures, suggesting that low LT50 values were probably due to the production of these compounds. This is the first report to characterize volatiles from FS0, FS1 and FS2 cultures of entomopathogenic fungi; its utility in different aspects opens an interesting area for further investigations.